Title: USA researchers learn why invasive plants are spreading rapidly in forests
[Penn State Live:Thursday, December 10, 2009] University Park, Pa. -- Invasive plants are advancing into Eastern forests at an alarming rate, and the rapid spread has been linked by researchers in Penn State's College of Agricultural Sciences to forest road maintenance and the type of dirt and stone used on roads. Perhaps predictably, according to David Mortensen, a professor of weed ecology who has been studying the spread of invasive plants for nearly two decades, humans are unwittingly accelerating the relentless march of invasives into even isolated forests. The findings are especially significant in the face of massive forest road-building efforts expected to support greatly expanded natural-gas drilling operations into the Marcellus shale formation. Hundreds or even thousands of gas wells could be established in Eastern forests in the next few years, depending on the market price of gas.
In a paper titled "Forest Roads Facilitate the Spread of Invasive Plants," published in the August 2009 issue of Invasive Plant Science and Management, Mortensen detailed some eye-opening revelations about the process by which invasive plants advance so quickly.
"Roads can play a profound role in the spread and growth of invasive species by serving as corridors for movement and by providing prime habitat for establishment," Mortensen explained. "For example, forest managers have reported that the borders of hundreds of miles of forest roads have been invaded by Japanese stiltgrass in a period of less than 10 years."
Japanese stiltgrass (Microstegium) is spreading rapidly in Pennsylvania forests.
As part of his research, Mortensen -- who was assisted by post-doctoral researcher Emily Rauschert and doctoral candidate Andrea Nord -- performed a large-scale survey of the presence and abundance of 13 invasive plants and found that the most abundant species, Microstegium (Japanese stiltgrass) is strongly associated with proximity to roads. He then focused his attention on trying to determine the reasons and devise a strategy to slow the spread.
The researchers discovered, to their amazement, that Japanese stiltgrass on its own does not spread quickly. To better understand why the invasive plant is achieving such a high rate of spread in Eastern forests, they deliberately introduced Microstegium patches in a forested site similar to the one in which the survey was conducted and allowed patches to naturally expand over four years before controlling all patches.
"Through this multi-year study, we found the natural spread rate was surprisingly slow, several orders of magnitude slower than that observed by the forest managers we work with," Mortensen said. "We also found that spread was greatest in habitats adjacent to forest roads.
